Many vehicles of all types often use metals and metal alloys (referred to herein interchangeably), particularly stainless steel and aluminum alloys, without any protective coating of a paint or a similar material, because of the aesthetical appeal of the natural metallic luster. Examples include aluminum alloy wheels for automobiles; various alloys of aluminum or stainless steel for gasoline tanks, trim and exhaust pipes for large trucks, and various alloys of aluminum or stainless steel for parts and trim on boats and ships. The metallic luster may be marred by accumulated soils of various types, including: oily soils, mineral soils, innumerable types of organic and inorganic matter, mud, tar, grease, oil, and virtually any other item which may be found in a transportation environment, for automobiles, trucks, trains, boats, and ships. Additionally, the metal alloys may become tarnished or otherwise lose their brilliance by build-up of natural oxide layers from the environment. As a consequence, periodic brightening is necessary to maintain the aesthetic appeal of these metallic surfaces.
Metal alloys, particularly aluminum alloys, may be brightened through microscopic or otherwise moderate etching, in which a selected composition or solution reacts with the metallic surface and removes a microscopic layer of the metal. Prior art alkaline and/or acidic solutions may have the unwanted result of irregular, non-uniform etching of the aluminum, with the potential for leaving pits or pock marks on the aluminum. In addition, such prior art alkaline and/or acidic solutions do not provide an effective means to control the etching rate and, again, produce irregular, non-uniform etching of aluminum and other metallic surfaces.
Prior art alkaline and/or acidic solutions used in the aluminum brightening process also require high concentrations of surfactants and other components. See, e.g., U.S. Pat. No. 4,762,638, discussed below. In order to improve etching performance, increased concentrations of all or most components are required, resulting in solutions having higher total concentrations in order to reach a desired rate of etching. These higher concentration solutions result in higher material costs, without providing adequate or sufficient performance for aluminum brightening.
Prior art acidic solutions used for cleaning and/or aluminum brightening typically contain a mineral acid, such as hydrofluoric acid (HF). These hydrofluoric acid detergents are highly corrosive, both to the vehicle and to the vehicle wash facility, are toxic to consumers and the environment, are dangerous to make, ship, and use, and may be otherwise damaging to a vehicle's surface.
Prior art alkaline solutions also may have the further unwanted effect of damaging other, adjacent surfaces. Use of those solutions requires masking of these other surfaces, such as glass or paint, prior to the application of such prior art alkaline solutions. Considerable time and effort is required to perform the masking, resulting in increased costs, and an increased risk of damaging these other surfaces.
A need remains, therefore, for a composition which provides brightening and cleaning for aluminum and other metals, with controlled and uniform etching in a relatively short period of time, such as the several minutes of a commercial vehicle wash. The composition should be nontoxic, and should not adversely affect other surfaces, such as painted surfaces, that may be in close proximity to the aluminum or other metal. In addition, such a composition should also have a cleaning effect for these other surfaces. Furthermore, a need remains for a low concentration solution which performs as effectively, or even more effectively, than current, prior art high concentration solutions.